All the factors are found when the next value is part of a pair that has already been identified. The difference is 3. The 3rd multiple of seven is 7 × 3 = 21. The 4th multiple of six is 6 × 4 = 24.

A prime number has exactly two factors, itself and one. The first ten prime numbers are \({2}\), \({3}\), \({5}\), \({7}\), \({11}\), \({13}\), \({17}\), \({19 ...